This invention relates to the production of aromatic mono- and polycarboxylic acids and, more specifically, to the hydrolysis of aromatic mono- and polynitriles to the corresponding aromatic mono- and polycarboxylic acids in a novel operation.
Catalytic conversion of aromatic hydrocarbons to aromatic polynitriles, as xylenes to benzodinitriles, is known. Suitable conversions are described in U.S. Pat. No. 3,479,385, for example. Hydrolysis of the benzodinitriles to the corresponding benzene dicarboxylic acids has also been described in application Ser. No. 551,013, filed May 18, 1966. By integrating the catalytic conversion and the hydrolysis process, it is possible to prepare a polynitrile, purify and then hydrolyze the latter by hydrolysis. For example, p-xylene is converted to terephthalonitrile which is then purified and the purified nitrile is subjected to hydrolysis. Terephthalic acid is recovered from the resulting hydrolysis product for use in the manufacture of resins and fibers.
The overall reaction involved in hydrolysis of terephthalonitrile is: ##SPC1##
Processes presently in use for hydrolyzing nitriles to the corresponding acids are carried out in two steps. First, the nitrile is partially hydrolyzed to a salt, ester, or amide, which is then converted, by hydrolysis or other means, to the carboxylic acid. Such processes can be costly to use because they require two sets of hydrolyzing equipment, including vessels, pipes, instruments, etc. For example, see U.S. Pat. Nos. 2,979,526 and 3,031,500 of Gasson, et al.
In accordance with the present invention, there is provided a single-step process for the production of an aromatic mono- or polycarboxylic acid by hydrolysis of its corresponding aromatic mono- or polynitrile, which comprises maintaining an aqueous slurry containing the aromatic nitrile, water and a minor amount of a catalyst selected from the group consisting of alkali and alkaline earth metal hydroxides, carbonates and salts of the aromatic carboxylic acids, and ammonium salts of said acids, at a temperature of from about 300.degree.F to about 600.degree.F for a sufficient time interval to hydrolyze substantially all of the aromatic nitrile to a hydrolysis product thereof containing the aromatic carboxylic acid and partially hydrolyzed aromatic nitrile and stripping ammonia from the hydrolysis product by contacting the product countercurrently with steam. The product is then cooled to a temperature of from about 100.degree.F to about 300.degree.F, whereupon the aromatic carboxylic acid precipitates out. The alkali metal, alkaline earth metal and ammonium salts of aromatic mono- and polycarboxylic acids are effective catalysts for the hydrolysis of the nitriles to the corresponding acids.
The process of this invention permits production of carboxylic acids from nitriles using less equipment than was heretofore required. Consequently, the utility requirements are also lowered.